Railway signal system



F. H. NICHOLSON RAILWAY SIGNAL SYSTEM Nov. 7, 1944.

Filed March 8, 1941 2 Sheets-Sheet [NVENTOR Nwlzolmzz aw H125 ATTORNEY Nov. 7,-1944. F. H NICHOLSON RAILWAY SIGNAL SYSTEM Fired March-8, 1941 2 Sheets-Sheet? a u. D W k m M J. 1 i s a 2 H PFI W? "m Fly-.115.

H15 ATTORNEY Patented Nov. 7,- 1944 RAILWAY SIGNAL SYSTEM- 1 Frank H. Nicholson, Penn Township, Allegheny v County, Pa., assignor to The Union Switch &

Signal Company, Swi

' of Pennsylvania ssvale, Pa., a corporation Application March 8, 1941, Serial No. 382,431

a 12 Claims. ('01. 246-33) My invention; relates, to railway signal systems, and it has reference to signal systems of the class employing coded track" circuits for controlling either or both wayside signals and train carried cab signals. More particularly, my invention relates to A. P.-B. and other systems for governing traffic inboth directions on a'stretch of single track railway, wherein the use of line wires usually employed in such systems is obviated by utilizing track circuits operating on the coded feed back? principle of United States Letters Patent No. 2,021,944 granted to me on November 26, 1935, for Railway traffic controlling systems. v

It has been proposed heretofore toprovide non-, line wire A. P. B, systems by utilizing track circuits incorporating the fcoded feedback principle above mentioned. One such system is dis closed and claimed in. -a copending application, Serial No. 294,897,;filed on September .14, 1939, by Ralph R. Kemmerer and assigned to the assignee of the presentlapplication, now Patent No. 2,280,491 dated April 21, 1942, and it is to be understood that certain features shown in the present application are covered inthe said Kemmerer application. Other features shown in the present application are covered byianother copending application Serial No. 352,936, filed on ject of mypresent invention is to provide novel and improved systems of the class exemplified by the aforesaid Kemmerer application,

Another object is to provide novel and im- I proved systems of the above described class which have increased utility and broader ranges of application.

A further object is to provide novel and improved systems of theabove described class'and 'incorporatting track circuitmeans operatingon stretch irrespective of the directiog lowing description, are attained in accordance with my invention by providing each section of a track with two track circuits, one for each direction of traffic movement over the section. One of the track circuits of each section normally is suppliedwith master code energy of the type effective tooperate the usual decoding apparatus insthe wayside or on a train; while the, other track circuit of the section is suppliedwith'another type of code energy. Suitable means responsive to the master code and to the other, code are provided for each'section, and wayside signals may be provided for each sectionand be controlled by such code responsive, means. Directional meansresponsiveto the direction of traffic on the stretch also are provided and, ar'- ranged to control the type of code supplied to the two circuits of each section in such manner as tov feed master code energy to each section always in the direction toward a train on the of movement of such train, and which directio al means also are effective to control. the supply of track circuit energy to the sections for. establishing directional control of traflic on the stretch to prevent opposing trafiic. movements-while permitting following movements in the established traffic direction.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel/features thereof in claims.

In the accompanying drawings, Figs. laand 127, when placed side to side with Fig-1a on the left, constitute, a diagrammatic view illustrating apparatus and circuitscomprising a portionof an absolute permissive block ,signal'system arranged in accordance with my invention.

Referring to the drawings, a stretch ofv single track railwayis represented-as divided by inthe coded feed backfprinciple'so arranged as to efiect the control of a greater number of signal aspects or indications than can be obtained 'in the systemsdisclosedin the said K emmererapplication. I

An additionalobject is to provide; novel and incorporating means'arranged to eifect the control of either or both wayside signals governing :jec'ts and characteristicfeatures of my invention 'awhichwill become readily apparent from the folimprovedsystems of-the-abovedescribed class sulated joints 2 intov a plurality of successive adjoining track sections A, B and C. 4Therepresented stretch is. to be understood as comprisingv a portion of the single track over which trains move in either direction betweenpassing-sidings I or double track portions which are not shown in the drawings. 1

The single track portion represented in the drawings is provided with apparatusembodying my invention arranged to provide a signal system for governing trafiic in both directions: and incorporating the usual absolute permissiveblock feature rendered effective when a train enters the single .trackportion, to prevent opposing trafiic movements-over such stretch while permitting:

one or more trains to follow the first train through the stretch at the [usual following .distance, In

The apparatus represented at a typical inter mediate signal location, as at location III in the drawings, comprises a pair of signalsone of which is designated by the reference character SE with a suitably distinguishing sufiix and governs eastbound traflic, and the other of which is designated by the reference character SW with a suitably distinguishing suffix and governs westbound trafiic.

which lamps when illuminated indicate clear,

"approach and stop, respectively. The ap paratus at each intermediate signal location also includes apparatus hereinafter described suitable for controlling the associated two signals and the supply of track circuit energy to the two sections adjacent each location. This apparatus comprises in general two track relays one incorporated into a track circuit provided for the section governed by the eastbound signal at such location and the other incorporated into a track circuit provided for the section governed by the westbound signal at the same location. Since the signals located at the: left-hand ends, as viewed in the drawings, of the sections are employedto govern eastbound traffic and these signals are in turn controlledby the track relays located at such left-hand ends of the sections, I shall refer to all track relays located at the lefthand ends of the sectionslas being eastbound track relays. The track relays located at the other or right hand ends of the sections accordingly will be termed westbound track relays.

In accordanee with my invention, each of the sections of track is provided with two track circuits one .for each direction oftrafiic. One of the track circuits of each section is arranged so as normally to effect control of railway traffic controlling apparatus such as wayside signals and train-carried cab signals, while the other of the track circuits of such section is arranged so as normally to detect an energized or deenergized condition of the circuit. This arrangement com prises normally supplying to one of the track circuits of each section coded track circuit energy of the type, which I shall term master code energy, adapted to be distinguished, in accordance with the rate of coding such energy, by the usual frequency codedecoding apparatus in the trackway or on a train, while normally supplying to the other track circuit of such section coded track circuit energy of another type, which I shall designate detector code energy, effective to be detected by the usual frequency code decoding apparatus but ineffective to be distinguished by suchapparatus in accordance with the rate of coding of such energy. The one track circuit of each section that is normally supplied with master type code energy includes a master code following relay, designated by the reference character TR and operable by such master type code energy, while the other track circuit of each section that is normally supplied with detector type code energy includes another track relay, designated by the reference character TRA and operable by either detector or master type code energy. I

. More specifically, each section is normally sup- These signals maybe of any suitable form and as shown comprise three-indication signals having a plurality of lamps G, Y and R,

plied at one of its ends with master track circuit energy coded at one or another of a plurality of rates or frequencies. These different code rates are comprised of recurrent code cycles each consisting of one on and one off interval when energy does and does not flow respectively, and these codes are differentiated from one another in accordance with the frequency of occurrence of the code cycles constituting such codes and hence are of the type commonly termed frequency codes. The other end of each of the sections is normally supplied with detector code track circuit energy of the feed back code type comprising energy coded at the rate corresponding to the rate of coding the master energy of the same section, and constituted of code cycles each comprising one on and one olf interval when energy does and does not flow respectively. In accordance with the feed back principle, the feed back code energy fed to a section is arranged so as to have the "on intervals of such code occur during the off intervals of the master code of the Section, while the 01f intervals of the feed back code occur during the "on intervals of the master code. I

In the drawings, the master code energy is represented as being normally supplied to each section from a master code source, such as a source of alternating current indicated by the reference characters BX and CK. For example, section B is supplied at its end III with master code energy from a transformer TTE which has one winding 5 connected to the rails of the section and has its other winding 6 supplied with energy from the source BX-CX at such times as contact 1 of a code repeating device CP is in its upper or front position. The device CP is at times caused to operate its contact I at one or another of the usual code rates or frequencies in a manner to be made clear presently, and it follows that the master code energy supplied to section B is therefore coded at one or another of the usual code frequencies in accordance with the rate of operation of contact 1 of device CP. For the purposes of this description, I shall assum that device CP at times operates its contact I at the rate of '75 or 180 times per minute, although it is to be understood that additional and/or different .rates of operation of contact .1 of device CP may be employed if desired. For example, in three-block, four-indication signal systems it is customary to employ three distinctive rates of coding and in such systems the code repeating device CP may be operated at one or another of three different rates suchas '75, and times per minute.

The master code energy supplied to-section B is conducted through the track rails to the other end of the section to operate the associated master code following relay TR. This relay is supplied with energy derived from the rails through themedium of 'a transformer TTW which has one winding 8 connected to the rails and has its other winding 9 connected when contact 10 of a code repeating device RC, hereinafter mentioned, is in its released or back position, to the input terminals of a full-wave rectifier which has its output terminals connected to the terminals of relay TR. Track relay TR. accordingly responds to the on intervals of the master code energy in the track rails, and such relay is provided with the usual frequency code decoding apparatus comprising a decoding transformer DTE and a plurality of decoding relays one for each of the different rates of coding the master code energy. To accord with the heretofore assumed two code rates of 75 and 180 cycles per minute,

relay TR is'represented in the drawings as being provided with two decoding relays, designatedby the reference characters H and D each having a suffix E to indicate that these relays are associated with an eastbound track relay. Relay TR controls the energization of primary winding ll of transformer DTE in the usual manner, and the supply of energy from the transformer secondary winding I2 to relay HE is controlled by relay TR through the medium of its contact l3 in a manner similar to that shown and claimed in a copending application, Serial No. 210,744, filed by myself and Leslie R. Allison on May 28, 1938, now

' Patent No. 2,237,788 granted April'8, 1941; hence relay HE is picked up whenever relay TR follows 75 or 180 master code. Relay 'I- IE therefore functions as a code detecting relay since it is picked up whenever the associated track relay follows any master code in the track circuit. Relay DE is energized from transformer DTE through the usual decoding unit IBUDU effective to permit relay DE to be picked up when and only whenthe associated'track relay'TR responds to, master energy coded at the 180 code rate. Relay DE therefore functions as a code selecting relay since it is picked up when and only "when'the' associated track relay operatesat the 180' code rate.

The decoding relays HE and DE] control in the usual'manner eastboundsi'gnal SEII'loc'ated at II and governingtraffic in the associated section. That is, signal SEII is caused to display its clear indication when both relays HE andDE are picked up; the signal displays its approach indication when relay HE ispicked up but relay DE is released; and when both relays HE and DE are released the signal is caused to display its stop indication.

The feed back code energy is represented as being supplied to each section-from a feed back' source, suchas a source of alternating current designated by the reference charactersBK and OK, but at times this source functions as a source of "master cod energy, as will be made clear presently. Section B, for example, is normally supplied at end II with feed back code energy from transformer TTW, which has its winding 9 supplied with energy from the source BKCK at such times as contact ll) of code repeating device RC is in its upper Or front position. Code repeating device RC is caused to operate. its contact ID at one or another of the usual coderates or frequencies in a manner to be. made clear presently, and it follows that the feed back code energy supplied to section B is therefore coded at one or another of the usual code frequencies in accordance with the rate of operation of contact ID of device RC.

The feed back code energy supplied to section B is conducted through the track rails to end III of the section to operate the associated feed back code following track relayTRA, which'follows the onflintervals of the feed back energy in the rails of the section. The on intervals of the feed back code of the section, as pointed out heretofore, occur during the 'ofi 'intervals of the master code energy in the same section, hence contact 7 of code repeater'CP at III is in its released or back position during each on in terval of the feed back energy in section B, and relay TRA accordingly is connected to winding of transformer TTE through this back contact of device CP' and a rectifier during each on interval of the feed back code energy. Relay TRA'picks up in response to each on interval ofthe feed back code, and completes an auxiliary stick circuit, hereinafter referred to, which functions to holdrelay TRA energized-until device CP operates its contact 1 to its upper or front position to supply an on interval of master code energy to the section.-

Relay TR-A at'III is provided with the usual frequency code decoding apparatus :which substantially corresponds to ,the apparatus heretofore described as being associated with relay TR. at II. The decoding apparatus associated with relay TRA have the suflixe's Win their respective reference characters toindioate the association of such apparatus with-awestbound track relay, and such apparatusdiifers from that shown associated with master code following relayTR at II in-that it is arranged normally to detect the presence of feedback code energy in the section but not to detect the rate of coding ofsuch energy, hence the associated code selecting relay DW is connected to the associated decoding transformer DTW only when the; code detecting relay'I-IE, associated with the eastbound track relay at the same location and associated with the next adjacent section C, is released to close its back contact I6. g

The decoding relays DW and. HW'associate'd with relay TRA of section B control in the usual manner the associated westbound signal SWIII located at III and governing traffic in section' B. This Signal is normally held at approach, as will be made clear presently.

From the foregoing, it is readily apparent that each of. the insulated track sections is provided with an eastbound track relay located at the left-hand end of the section, and a westbound track relay located at the right-hand end of the section.- These eastbound and westbound relays are each provided with decoding :apparatus for controlling respectively eastbound and west hand end of one section and the left-hand end of an adjacent sectiommay be considered as be ing provided with decoding apparatus associated with an eastbound track relay incorporated into the eastbound track circuit provided for the sec- 7 tion extending to the east orto the right, as viewed in the drawings, of the signal location, anddecoding apparatus associated with a westbound track relay incorporated into the westeastbound track relay at such signallo'cation,

and the other relay WS associated with the westbound direction and hence associated with the westbound'track relay at the same signal location. These stick relays are suitablycontrolle'd merer application Serial No. 294,897.

the two track relays at. each intermediate signal lccationcooperate in controlling the relays ES and WS in such manner that the relays are normally released; that relay ES is picked up when an eastbound train enters the section governed by the associated eastbound signal and is maintained picked up until such section is vacated; and that relay WS is picked up when a westbound train enters the section governed by the associated westbound signal and such relay is, maintained picked up. until such section is vacated. This control of the stick relays is. ef-

fected by providing each directional stick relay with a pick-up circuit and a stick circuit, which circuits are represented in the drawings in the form of written circuits wherein certain contacts forming a part thereofare represented remote from the relays causing such contacts to operate. Each of such contacts has, however, been identified not only by a referenc character individual to such contact, but also by placing above such contact the reference character of the relay causing such contact to operate. Contact 38,, for example, bears the reference character HE to indicate that this contact is controlled byrelay- HE. These circuits further involve the use of repeater relays, designated by the reference character P with a suitably distinguishing suffix, one for each of the two signal control relays H at an intermediate signal location. Relay HE at II, for example, has a repeater relay PE associated therewith and controlled over a circuit extending from one terminal of the source. through contact 3'! of relay TR (closed in the released position of the relay), front contact 38 of relay HE, the winding of relay PE and back contact 39 of relay WS at 11 to the other terminal of the source. Relay PW at II is similarly controlled by back contacts 40 and 42 of relays TRA and ES and front contact 4|, of relay HW, as is readily apparent from an inspectionof the drawings. Each of the relays PE and PW has a resistor 43 connected across its terminals for providing slow releasing characteristics which makes each relay P slower in releasing thanits associated H relay.

The pick-up circuit of relay ES at II may be traced from one battery terminal through back contact 44 of relay PW at II, back contact 45 of relay HE at II, front contact 46 of the associated repeater relay PE and the winding of relay ES; to the other battery terminal. Relay ES. when picked up completes an obvious stick. circuit which includes its own front contact 48 connected around front contact'flli of relay PE. The pick-up circuit for relay WS at H is similar and it includes a source of current and back con-. tacts 50 and of relays PE and HW and front contact 520i relay PW. The stick circuit of relay WS at II includes its own front contact 54, in the place of front contact 52 of relay PW.

The apparatus at each signal location fur-a ther includes code generating means effective to generate one or another of a plurality of code rates. In the particular system illustrated, it has been assumed that only two code rates are utilized hence the code generating means are etfective to generate the two assumedcode rates or '15 and 180 code cycles per minute. These code generating means, may be of any suitable form but as shown comprise two constantly energized code transmitters or coders, L'iCT and l8llCT; Coder 150T is. provided with contacts and 15a; which are, operated at a rate of 75. times per minute alternately into and out oi engagement tag and time which are operated at the rate. Qi-

180 times. per m nute alt rnately in o and. out or ncasem nt. with the respe ti e fr nt contact points. These coders G'I. ar r nged in. ac..- cordance with the, customary practice, in such. mannerthat the cont members, of, say, coder 750T are alternately held first into and. then out of engagementv with their associated front contact points for intervals having substantially equal durations, and the contact members of coder MCT are likewise operated alte nate yinto and out. or engagement with their associated front contact points for intervals also haying; substantially equal durations, the durations of the intervals formed by the operation of, coder IKllCT of course dif ering from those formed by th operation of coder 15017. It follows that any one of such contacts is .efiective when interposed in. a Circuit. supplied with energy, to periodically interrupt, or code. such energy at a rate corresponding to the, rate, of operation of such con, tact, and that the codes generated by such coders comprise recurrent code cycles each comprised of an on interval and an off interval having substantially equal durations for a/given code e. These odes are, theref r f he frequen y code type.

At locations where master code energy is supplied to the rails of one of the adjacent. sections,

'as at location III where the eastbound track circuit of section B is supplied with master code energy, the code transmitters T and IBIICT. are operative to code the supply of such energy to the track rails in accordance with the traffic conditions on the stretch. That is to say, when the stretch is unoccupied so that the apparatus' I is in its normal condition as represented in the drawings, code repeating device CP at III is cn-. ergized over a circuit extending from. one terminal or a suitable source of unidirectional current,

'such as a battery not shown, through contact,

of section C is picked up, device CP is energized over a circuit extending from on terminal of the unidirectional source through contact 15a, of coder 150T; front contact E8 of' eastbound; sticl; relay ES associated with section C, back contact H of relay HE associated with section C, and the Winding of device GP to the other terminal of the source At such times, therefore, device C1? operates at. the 75 code rate to code at this rate the energy supplied to transformer TTE.

At; locations where feed back code energy is normally supplied to the rails of one of the ad- .iacen-t sections, as at location II where the westbound track circuit of section B is normally supplied with such feed back code, the decoding apparatus provided for the master code following track relay TB of such section at that location is arranged to control the supply of such feed back code to. the associated section. Referring; to location II, for example, the previously mentioned code repeating device RC associated with section B is normally supplied with energy from a transformer 20 which has its secondary winding 2| connected to device RC through an obvious circuit including front contact 22 of relay HE of the associated section and a back contact 23 of the associated eastbound stick relay ES. The primary winding 24 of transformer 20 is connected, through front contact 26 of the code detecting relay HW at location II associated with the adjacent section A, to a secondary winding 25 provided for the associated decoding transformer DTE. At times,=however, the connection of winding 25' of transformer DTE to winding 24 of transformer 20 is effected through an auxiliary circuit including back contact 26 of relay HW of section A and front contact 21 of westbound stick relay WS associated with sec-' tion A. The device RC preferably is of the type shown in the copending application Serial No. 358,319 filed by Herman G. Blosser on September25, 1940, for Reissue of Patent No. 2,174,255, now reissue Patent No. 21,783xdated April 29, 1941. This device responds only to energy having the polarity indicated by an arrow placed on device RC, and which I shall term ositive polarity, and hence is actuated only when its left-hand terminal is positive with respect to its right-hand terminal. Energy of such positive polarity (indicated by an arrow associated with transformer 20) is induced in winding 2| of transformer 20 and is supplied to device RC when the associated track relay TR releases and :closes its back contact 28 to induce in winding 25 of transformer DTE an impulse of energy. When the just described circuits of the primary and secondary windings of transformer 20 are complete, each release of relay TR causes the induction of a positive impulse of energy in transformer secondary winding 2|, and eachof these impulses is transmitted to device RC and produces a'momentary pick-up of that device so that its contact I is operated from its back to its front position. This operation of device RC disconnects the associated track relay TR from transformer TTW and connects the feed back source BKCK to such transformer, thereby causing to flow in therails of the associated section a relatively shortimpulse of feed back code energy. I I v As pointed out heretofore, master code following relay TR of section B normally operates at the 180 code rate in response to master code energy coded at the 180 code rate available in section B, hence the feed back'code supplied to such section is normally codedat the 180 code 1 maintains such relay in its picked-,up position until the occurrence of the next on interval of the master code supplied to the associated section, this circuit extending from one terminal of the unidirectionalvsource through front contact 30 of the [code detecting relay HE at III associated with sectionC, front contact 3| and the winding of relay TRA, and back contact 32 of device CF to the other terminal of the source.

The operation of relay TRA by feed back energy coded at the 180 code rate isof course detected by the associated code detecting'relay HW, which is caused to be picked up when the associated track relayTRA follows feed back code energy,

but the code selecting I 'relay DW associated therewith is normally released since it is energized only when ,codedetecting relay HE at III associated with the adjacent section C is releasedto close its back contact l6, as pointed out heretofore. Asshown, signal SWIII controlled by relays HW and DW'at III thus may be normally caused to display its approach indication.

At times, however, the signa1 normally held at approach by a track circuit supplied with feed back code energy may be cleared by replacing the feed back code energy of such track circuit with track circuit energy of' the master code type. This results when the master code operated track relay TB of a section becomes inactive and holds. its contacts continuously in their released positions, and the stick relay associated with that track relay is also released. If relay TR at II is "inactive so-that its associated code detecting'relay HE is released, and theassociated up under the above assumed conditions, device RC is energized over a circuit extending from one terminal of the unidirectional source through contact I of coder I80CT, front contact 34 of relay HW associated with section A, back confected when code repeating device CP at III is caused to supply master track circuit energy coded at the 180 code rate to section B in response to energization of device CP over its previously traced circuit including contact IBDa of coder I80CT. It follows, therefore, that when device RC at His energized overthepreviously traced circuit including contact 180 of coder I80CT, the energy supplied from transformer TTW-to the rails of section B at II substantially corresponds to the master code energy normally supplied to section B at III by code repeating device CP, hence the energy supplied from transformer TTW to section B under such assumed conditions may be termed master code energy since it is of the frequency code type.

-Whenever relays HW; HE and ES at II are released and the associated westbound stick relay WS'is picked up, code repeating device RC at II is energized over a circuit jextendingfrom one terminal of the unidirectional source through contact 15 of cedar T, .front contact 35 of westbound stick relay WS associated with section A, back contact 34 of relay HW associated with section A, back contact 22 of relay HE associated with section B, back contact23" of eastbound stick relay ES associatedwith section B and the wind- ,ing'of device RC to the other terminal of the source.- At such timesytherefore, deviceRC operates'at the '75code rate to cause master code energy coded at the '75 code rate and of the frequency code type to be supplied at II to the rails of section B. It is, of course, obvious that when'master code energy is substituted for feed back code energy in of the train movement.

in substantially the same mariner that the master code following relay TB of the same section normally responds to the master code energy supplied to its associated track circuit.

In the drawings, the sections or portions thereof illustrated are represented as being provided with eastbound track circuit apparatus arranged normally to utilize master code energy and westbound track circuit apparatus arranged normally to utilize feed back code energy. showing is of course merely illustrative, and it is to be understood that for any section intermediate the two end sections of the stretch, the master code energy may be utilized for either the eastbound or the westbound track circuit of such secbe arranged to feed'master code energy in op-' posite directions in such section.

The apparatus, as pointed out heretofore, is

arranged so that with the single track stretch between passing sidings unoccupied, the master code energy supplied to each section is coded at the 180 code rate and the signals governed thereby are caused to display their clear indications,-

while the feed back code energy supplied to each section is likewise coded at the 180 code rate but the signals controlled thereby are caused to display their approach indications. It follows, therefore, that each signal normally displays either its clear or its approach indication according as such signal is normally controlled by master or by feed back code energy, respectively.

The apparatus embodying my invention is arranged in such manner that when a train enters the single track stretch and shunts the rails of the first section, all of the remaining sections of the stretch are deprived of the track circuit energy that is normally supplied to the track circuits associated with the direction opposite that Additionally, the apparatus functions in such manner that if any of such remaining sections is deprived of track circuit" energy of the master code type due to a train entering the stretch, the feed back code energy that is normally supplied to the other track circuit (associated with the direction of the train movement) of such section is replaced with master code type track circuit energy. In other words, whenever a train enters the stretch the apparatus functions to control the supply of code energy to the circuits of each of the sections in such manner that in each of such sections, the one track circuit associated with the direction f movement of the train is supplied with master code track circuit energy;

In the sections where master code track circuit energy is supplied to the circuits associated with the direction of train movement and feed back code energy is supplied to the circuits associated This which is available when the eastbound train is inactivity of the other track relay of the section not only causes the display of the stop indication of the associated signal which governs opposing trafiic movements in the section, but also functions to cause all of the opposing signals, up to the next headblock signal, to display their respective stop indications, by causing the successive deenergization of the track circuits governing such signals. For example, if an eastbound train enters section A at the left-hand end, as viewed in the drawings, of the represented stretch, all the westbound track circuits, that is, the track circuits controlling the track relays of the stretch positioned at the right-hand ends of the sections, are deenergized and all westbound relays are inactive. Under such assumed conditions, westbound track relay TRA of section A is shunted and is inactive, relay HW associated therewith is released to cause signal SWII to display its stop indication, repeater relay PW releases, and front contact 26 of relay HW opens to interrupt the previously traced circuit of primary winding 24 of transformer 2|] so that code repeating device RC at II is maintained steadily deenergized and the supply of feed back code to section B is discontinued. Relay TRA of section B accordingly becomes inactive, relay HW associated therewith releases to cause signal SWIII to display its stop indication, repeater relay PW at III releases, and the circuit of transformer 20 is opened at front contact 26 of relay HW to constantly deenergize code repeating device RC and thereby remove feed back code energy from section C.

The inactivity of relay TRA of section B and the release of its associated decoding relay due to an eastbound train on the stretch does not at this time have any effect upon the supply of master code energy to section B, so that relay TR of this section responds to the 180 code master energy supplied to the section and signal SEII is held at clear. Likewise, section A is supplied at location II with 180 master code energy in the section to operate train-carried apparatus on the train. This apparatus may, for example, be of the type shown in United States Letters Patent No. 1,773,515 granted to C. C. Buchanan on August 19, 1930. If such apparatus is employed on the train, a clear cab signal indication will of course be provided in response to the 189 master code energy available in section A.-

When the eastbound train passes location II and enters section B, relay TR of that section is shunted, relays HE and DE associated therewith J are released, repeater relay PE becomes deenergized, signal SEII is controlled to its stop indication, and eastbuond stick relay ES is picked up over its previously traced pick-up circuit and is held up over its stick circuit after relay PE releases. With back contact II of relay HE and front contact N3 of relay ES at II closed, code repeating device CP at II is energized over its previously traced circuit including contact 15a of coder'IBCT, and 75-master code energy is therefore supplied to section A.

When the eastbound train enters section C, relay TR associated therewith is shunted, signal SEIII is operated to its stop indication, relay ES at III is picked up, and 75 code energy is supplied .tions to become inactive.

section A from the 75 to the 180 code rate. Stick relay ES at II releases when the associated relay relay TR of section B closing its back contact 28 at the rate of '75 times per minute in response to 75 master code energy in the section) to cause operation of relay TRA of section B at the 75 rate and pick up relay HW associated therewith. This action closes from contact 26 of relay HW interposedin the circuit of the primary winding 24 of transformer and thus conditions that transformer to transmit impulses of energy to the associated code repeating device RC at III When relay HE at III picks up and relay ES releases to complete the circuit of secondary winding 2| of such transformer.

Relay'I-IE at III is picked up and the associated relay ES is released when section C is vacated by the train and relay TR of that section responds to the 75 master code energy available in the section. Feed back code energy coded at the 75 code rate is therefore supplied to section C, while the master code energy supplied to section B is shifted from the '75 to the 180 code rate. Relay TR of section B of course operates at this 180 code rate to energize the associated decoding relays HE and DE and cause signal SEII to display its normal clear indication. The feed back code :2- energy supplied to section B is now coded at the 180 code rate, but since relay HE associated with section C is at this time picked up to open its "back contact IS, the operation of relay TRA of section B at this 180 code rate results only in the 'energization of code detecting relay HW but not of code selecting relay 'DW associated therewith. The associated signal SWIIIis therefore maintained in its normal approach condition.

It follows from the foregoin-g that the apparatus embodying my invention and represented in the drawings is arranged to incorporate the usual A. P. B. feature that becomes efiective when an eastbound train enters the stretch, to prevent opposing westbound movements over the stretch While permitting other eastbound trains to follow the first through the stretch at the usual followins distances.

In the sections having master code energy normally fed in the direction of traffic movement and feed back code energy fed in the direction toward the train moving on the stretch, or opposite in direction to the direction of the train movement, the shunting of the rails of the first section by'a train and-'consequent'removal of the energy (master'code) fed 'to a remaining section in the direction of a train movement on the. stretch not only results in placing the signal governed by such energy at stop, but also in reversing the normal track circuitarrangement so as to replace the feed back code energy normally supplied to such section with master code energy. For example, sections A, B and C are represented in the drawings as having track circuit apparatus arranged so as to feed master code energy toward an eastbound and away from a westbound train on the stretch. A westbound train entering the stretch will, therefore, deenergize the eastbound track circuits of the represented sections to cause the master code following relays TR of suchsec- Under such assumed conditions, master relay TR at III is thus rendered inactive and relay HEassociated therewith releases and opens its front contact 11, thereby opening the normal circuit of code repeating device CP at'III and consequently deenergizing the eastbound track circuit, normally fed with master code energy, of the adjacent section B. Relay TR of section B accordingly becomes inactive, signal SEII controlled thereby is caused to display its stop indication, and code repeating device CP at II is deenergized, thereby depriving'the eastbound track circuit of seotionA of master trackcircuit energy. In addition, when relay TR of section C becomes inactive due to a westbound train in the stretch, relay PE at III releases, and relay HE at III operates its contact 22 from its front position where it closes the previously traced circuit over which code repeating device RC at III is normally operated, to its back position where contact I of coder I80CT is interposed in a previously traced circuit of device RC. This results in'device RC being operated at the code rate in the manner such as to provide 180 master code track circuit energy to the westbound track circuit of section C. A similar action occurs at locationII, hence the Westbound track circuit of sec. tion 3- is supplied with 180 master code energy. Code repeating device CP at location III is steadily deenerg'ized since its energizing circuits are open with relays HE and ES associated'with section C both released, and back contact I of device CP remains constantly closed to connect relay TRA to transformer TTE. Relay TRA acsection Cis released and contact 30 operated thereby is held steadilyreleased to prevent the completion of such circuit. Back contact I6 of relay I-IEof section C is now closed to condition the decoding apparatus associated with relay TRA to'be effective to difierentiate between different rates of operation of relay TRA. It follows, therefore, that operation of relay TRA at the 180 code rate causes both relays HW and DW associated therewith to be picked up so that signal SWIII is cleared.

When the westbound train occupiessection C, the 180 master code energy supplied to the westbound track circuit of that section is of course available to operate train-carried apparatus on the train. When the train passes signal SWIII and enters section B, relay TRA associated therewith is shunted and the associated relays HW and DW release to cause signal SWIII to display its stop indication. Westbound stick relay WS at III now picksup over its previously traced pickup circuit, to complete at this time the previously mentioned auxiliary path that connects secondary winding 24 of transformer 20 to primary Winding 25 of transformer DTE. Code repeating device RC is now energized over a circuit previously traced and including contact 15 of coder CT15, so that as a result the westbound track circuit of section C is supplied with 75 master code energy. I

This 75 master code energy supplied at IIIto code to operate relay TR and pick up relays HE and DE associated therewith, and cause the westbound track circuit of section C to be supplied with 180 feed back code energy.

With relay HE of section C picked up, 180 master code energy is supplied at III to the rails of section B, but this energy is of course shunted away from relay TB of such section by the train. When the westbound train enters section A, relay TRA associated therewith is shunted, signal SWII is caused to display its stop indication, relay WS is picked up, and '75 master code energy is supplied to the westbound track circuit of section B to cause operation of relay 'I'RA at III when the train vacates section B. When this happens, therefore, the westbound track circuit of section B. is supplied with 75 master code energy, and code repeater CP of section B is energized at the 180 code rate and relay TRA of section B is intermittently connected and disconnected from transformer 'ITE at the 180 code rate. A portion of the on intervals of the '15 code energy supplied at II to the rails of section B is transmitted through transformer TTE to relay TRA during the intervals that device CP operates its back contact I closed, and relay TRA accordingly responds to such received portions of the 75 code to pick up the associated relay HW and operate signal SWIII to its caution position. With relay HW picked up, relay WS releases and relays PW and PE pick up.

Relay TR of section B is intermittently connected to and disconnected from transformer 'ITWat II at the '75 code rate due to the operation of code device RC at the '75 master code rate. The rails of this section are also supplied at III with 180 master code energy, and relay TR accordingly responds to a portion of such energy and picks up relay HE associated therewith to disconnect, at back contact 22, code repeater device RC at II from contact '15 of coder 150T. Front contact 22 of relay HE is now closed so that code repeating device RC is connected to secondary winding 2| of transformer 20. The primary winding of this transformer is connected to transformer 20 over its circuit path including back contact 26 of relay HW associated with section A and front contact 21 of relay WS, and repeating device RC accordingly is energized by pulses of energy which are induced in transformer 20 at the rate that relay TR of section B responds to the master code energy supplied at III. This master code energy is coded at the 180 code rate, hence reiay- TR follows this energy to cause both relays HE and DE associated therewith to be picked up, thereby causing signal SEII to display its clear indication and causing code repeating device RC to transmit 180 code feed back energy to relay IRA of section B. Relay TBA follows these pulses of feed back code,'and maintains relay HW picked up, but relay DW associated therewith is released since back contact I 6 of relay HE of section C is picked up. The apparatus v westbound track circuits, as pointed out heretofore. Assume that a westbound train occupies section A, and that the first train is being followed by a second. The second train causes the eastbound track circuits of sections B and C to be deenergized. so that relays TR of such sections are released. At location II, relay WS is picked upbut relay I-IW-is released due to the shunting of relay 'IRA of section A by the first westbound train, so that code repeating device RC at II is energized over its previously traced circuit including front contact 35 of relay WS and back contact of relay HW and contact '15 of coder 1501 at II. Master track circuit energy of '75 code accordingly is fed to the westbound track circuit of section B, and relay TRA at III in response thereto picks up relay HW associated therewith to operate signal SWIII to its approach indication. Code repeating device RC at III is now energized over front contact 34 of relay HW, back contact 22 of relay HE and contact of coder IBDCT at III, so that 180 master code track circuit energy is supplied to the westbound circuit of section C. This energy is of course available either to operate the associated westbound signal (not shown) of section C to its clear indication, or if the second train occupies section C, to operate the train-carried apparatus on the train to cause the display of its clear indication. It is readily apparent, therefore, that apparatus embodying my invention is arranged to incorporate the usual A. P. B. feature that becomes effective when a westbound train enters a stretch, to prevent opposing eastbound movements over the stretch while permitting other westbound trains to follow the first through the stretch at the usual following distances.

From the foregoing description, it is readily apparent that apparatus embodying my invention is arranged so as to provide each insulated section of the stretch of track with two track circuits, one of which is normally supplied with master type code energy effective to operate frequency type decoding apparatus and control either or both wayside and train-carried traffic controlling apparatus in accordance with the code rate of such energy, and the other circuit of which is normally supplied with feed back type code energy effective to operate a code detecting relay. It is further apparent that whenever a train enters the stretch, the track circuit energies supplied to the two circuits of each section are so controlled that in each of such sections the one track circuit associated with the direction of train movement is supplied with master type code energy, thereby effecting control of wayside signals governing trainc in the direction of the train movement and rendering effective train-carried traffic controlling apparatus on the train.

Additionally, it is apparent that inasmuch as the apparatus effects control of wayside and train-carried traffic controlling apparatus governingtraffic in the direction of a train movement on the stretch in response to master type Icode energy supplied to the track circuits associated with the direction of train movement, and

since by coding such energy at one or another of a plurality of code rates a plurality of distinctively different controls may be effected through the medium of. such energy, the number of indications or other controls of the traific controlling apparatus effected may be varied in accordance with the particular conditions of each application merely by varying the number of code rates employed. Thus, for example, apparatus embodying my invention has been illustrated and described in connection with a two-block threeindication signal system utilizing two different code" rates of master code energy, but it is evident that by employing a greater number of code rates together with decoding apparatus having means for detecting each of the different code rates employed, a, multiple-indication signal system having any desired number of indications desired may be provided; as for instance a threeblock, four-indication system is readily provided by utilizing three different code rates of master code energy and the usual frequency type decoding apparatus effective to differentiate the three rates of coding; I w

Although I have herein shown and described only one form of railway signal apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing 'from'the spirit and scope of my invention. h

Having thus described my invention, what I claim is: v

1. Track circuit apparatus for use with a-section of railway track supplied at one end thereof with track circuit energy coded at one. or another of a plurality of code rates, comprising the combination with a code following track relay and a code repeating device normally effective to couple said relay to the rails at the opposite end of said section and effective when operated to uncouple said relay from the rails and couple a source of current to such rails, a decoding transformer having a primary windingsupplied with energy over contacts of said track relay for inducing in the secondary windings of said transformer alternating electromotive forceshaving a frequency corresponding .to the rateof operation of said track relay, of a code detecting relay energized from a secondary winding of said transformer for detecting'a code following operation of said track relay, and means controlled by said code detecting relay for at times operating said code repeating device by energy induced in another secondary winding ofisaid transformer and at other .times operating said device by coded energy from another source. a l v 2. Track circuit apparatus for use with a section of railway track supplied at one end thereof with track circuit energy coded at one or another of a plurality of code rates, comprising the'conibination with a code following track relay and a code repeating device normally effective to.

couple said relay to the rails at the opposite end of said section and effectivewhen operated to uncouple said relay from the rails and couple a source of current to such rails, a decoding transformer having a primary winding supplied 'with energy over contacts 0f said track relay for inducing in the secondary windings of said transformer alternating electromotive forces having a frequency corresponding to'the rate of operation of said track relay, acode detecting relay energized from a secondary winding of said. transformer for detecting a code following operation of said track relay, and means controlledby said code detecting relay for at times operating said code repeating device by energy induced in another secondary Winding' of saidtransformer and at other times operating said device by coded energy from another source.

3. Track circuit apparatus for use with two adjoining track sections each supplied at their respective remote ends with track circuit energy coded at one or another of a plurality of code rates, comprising the combinationwith two code following track relays and two code repeatin devices one for each track relay and each effective normally to couple the associated relay to the rails of its associated sectionat the endgadjacent the other section and effective when operated to un- ,couple such relay, from the rails and couple to such rails a source of energy, of decoding means for each track relay selectively responsive to the rate of operation of theassociatedtrackrelay, means controlled by the decoding means associated with one of said track relays for rendering the other of said decoding means effective normally to detect code following operation of the associated other track relay but not todetect the rate of operation of such relay, code generating means normally effective to operate at one or another of said plurality of code rates the one of said code repeating devices associated with one of said track relays, and means-controlled by the deco-ding means ofthe other of said track relays for at times operating the other of-said code repeating devices at a rate corresponding tothe rate of operation of the said other track relay and at other times for operating said other code repeating device from said code generating means,

4. Track circuit apparatus for use with two adjoining track sections each supplied at their respective remote ends with trackcircuit energy coded at one or another of a plurality of code rates, comprising the combination with two code following track relays and two code repeating devices one for each track relay and each effective normally to couple the associated relay to the rails of its associated section at theend adjacent the other section and effective when operated to uncouple such relay from the rails and couple to such rails a source of energy,"'two decoding means one for each track relay and each including a decoding transformer having a primarywinding supplied with energy over-contacts of the associated track relay for inducing in the transformer secondary windings an alternating electromotive force having a frequency'corresponding to the rate of operation of the associated track relay,

said decoding means also each including a code detecting relay energized from the associated decoding transformer and picked up when energy having a frequency corresponding to any of said code rates is supplied thereto, two directional stick relays one for each track relay, code generating means normally efiective-to, operate atone or energy induced in the decoding transformer associated with the other'of saidtrack relays and at times to operate in response to energy supplied from said code generating means.

5. Track circuit apparatus for use with tWo adjoining track sections each supplied at their respective remote 'ends with track circuit energy coded at one or another of a plurality of code Irates, comprising the combination with two'code followingtrack relays and twocode repeating devices one for each track relay and each effective normally to couple the associated relay to the rails of its associated sectionat the end adjacent the other section and effective whenoperated to to the rate of operation of the associated track g t relay; said decoding means each also-including a plurality of decoding relays energized from the associated decoding transformer and comprising a code detecting relay picked up whenever energy having a frequency corresponding to any of said plurality of code rates is supplied thereto and a code selecting relay picked up in response to energy having a particular frequency corresponding to a selected one of said code rates is supplied thereto, means controlled by the code detecting relay of the decoding means of one of said track relays for at times conditioning the other decoding means to be effective to pick up the associated code detecting relay but not the code selecting relay irrespective of the frequency of the energy supplied to such relays two directional stick relays one for each track relay, code generating means normally effective to operate at one or an-' other of a plurality of code rates the one of said code repeating devices associated with one of said track relays, and means controlled by said two 3 code detecting relays and said two directional stick relays for normally causing the other of said code repeating devices to operate in response to energy induced in the decoding transformer associated with the other of said track relays and at times to operate in response to ener y supplied the section rails with recurring pulses of master code energy consisting of a plurality of impulses that are separated by ofi period intervals and means at the sections opposite end which respond to said master energy pulses that are there received from those rails, the second direction track circuit for each section comprising means at the sections said opposite end which during and only during reception of the sections said master code pulses at that end further supply the section rails with pulses of feed back energy that recur in step with the o periods or the received master code and means at the sections said given end which receive said feed back pulses from those rails, each said second direction track circuit having associated therewith supplemental means at the said opposite end of the section which come into operation only when the sections'said master pulses fail to be transmitted to that opposite end and which then supply the section rails with special code energy "in the form of pulses that are independent of the sections said master code oii periods and that are distinctive of traific conditions beyondthat opposite end, the combination with the foregoingv apparatus of means ef. fective upon theshunting of any sectionin said stretch by a. given-to-opposite end moving train to cause removal of the master energy from all sections between the train and the extreme opposite end of the stretch whereby thento replace the feed back energy in each of those sections with the said special code energy pulses by which tra'iiic conditions beyond the sections said opposite end are reflected.

7. In a signal system provided for a stretch of railway track divided by insulating joints into a plurality of successive track sections each provided with a first direction trackcircuit and a second direction track circuit, the first direction track circuit for each of said sections comprising track circuit for each section comprising means.

at the sections said opposite end which durin and only during reception of the sections said master code pulses at that end further supply the section rails with pulses of 'feed back energy that recur in step with the said off periods of the received master code and means at the sections said given end which receive said feed back pulses from those rails, the second direction track circuit of each section also including supplemental means at the said opposite end of the section which come into operation only when the sections said master code pulses fail to be transmitted to that opposite end and which then supmeans at the sections given end which supply 15 ply the section rails with special code energy in the form of pulses that are independent of the sections said master code "01? periods and that recur at a rate distinctive of traffic conditions beyond that opposite end, the combination with the foregoing apparatus of means effective upon the shunting of any section in said stretch by a given-to-opposite end moving train to cause removal of the master code energy from all sections between the train and the extreme opposite end of the stretch whereby then to replace the said feed back energy in each of those sections with the said special code pulses by which trafilcconditions beyond the sections said opposite end are reflected.-

8. In a signal system provided for a stretch of railway track divided by insulating joints into a plurality of successive track sections each provided with a first direction track circuit and a second direction track circuit, the first direction track circuit for each of said sections comprising means at the sections given end for supplying the section rails with recurring pulses of master code energy that are separated by 0 period intervals and that recur at a rate distinctive of trafiic conditions beyond that given end and master decoding means at the sections opposite end receiving said master code pulses and selectively responsive to each code rate at which such pulses recur, a second direction track circuit ioreach section comprising meansf'at the sections said opposite end effective when :and only when said master decoding means responds to said master code pulses for additionally supplying the track rails with pulses of feed. back energy that recur instep with said off periods of the sections master code and other decoding means at the sections given endreceivin'g said iced back pulses and including means selectivelyresponsive to each code rate at which pulses of energy are there received from said track rails, supplemental means at the said opposite end of each section rendered effective by the section s master decoding means when such means becomes inactive due to a removal of the -master code energy from the rails of the section for supplying the section rail with special code energy in the form of pulses that are independent of the sections said master code ofi periods and that recur at a rate dis tinctive of traflic conditions beyond that opposite end, and means governed by the track circuits of any section shunted by a given-tooppos'ite end moving train for causing the removal of the said master code energy from all sections betweenzthe train and the extreme opposite end of said stretch,

thereby to cause the feed back ener y in each of such sections to be replaced by said special code pulses by means of which traific conditions inad- .vance of the train are reflected.

9. In combination, a stretch of'railway track including a plurality of successive adjoiningtrack sections, a first direction track circuitfor each of said sections comprising means at the-sections given end for supplying the section rails with recurring pulses of master code ener y that are separated by offperiod intervals and that recur at a rate distinctive, of traffic conditions beyond that given end and master decoding means at the supplying the track rails with pulses of 'feed back energy that recur in step with said ofi periods of the sections master code, and other decoding means at the'sections given end receiving said feed back pulses and including means-selectively responsive to each'code rate at;which pulses'of energy are there received from said track rails,

means governed by the master decoding means at the said opposite end of each section for at times rendering the said other decodingmeans at the adjacent given end of the next adjoining section to be effective only to detect pulses of energy in' the rails of said next adjoining section and operative when such master decoding means becomes inactive when that sections master code pulses fail to be received at that sections opposite end to condition the next adjoining sections other decoding means to be effective to detect the ,code rate atwhich pulses of energy arereceived from the rails of said next adjacent section, supplemental means at the said opposite end of each section rendered eiTective by the sections master decoding means when such means becomes inactive ,due to a removal of the master code energy from the rails of the section for supplying the section rails with special code energy in theform of pulses that are independent of the sections said master code oiT? periods and that recur at a rate distinctive of traific conditions beyond that opposite end, and means governed by the track circuits of any section shunted by a given-toopposite end moving train for causing the removal of the said master code energy from all sections between the train and the extreme opposite end of said stretch, thereby to cause the feed back energy in each of such sections to be replaced by said special code pulses by means of which traflic conditions in advance of the train are reflected.

10. In combination, a stretch ofrailway track including a plurality of successive adjoining track sections, a first direction track circuit for each of said sections comprising means at the sections given end for applying to the section rails master track circuit energy coded at one or another of a plurality of code rates each comprising 'recurrent code cycles consisting of an on and an ofi interval during which energy is and is not present respectively in the section rails and master decoding means receiving energy from the section rails at the opposite end of the section and including means selectively responsive to the rate at which energy there received is coded, a second direction track circuit for each -section comprising feed back code transmitting means at the sections said opposite end controlled by the sections master decoding means andeffective when and only when said master decoding means receives master code energy from the section rails for applying to such rails pulses of feed back energy that occur in step with the off intervalsiof said master code energy and other decoding means at the sections said given end receiving energy from the section rails and includ- ,ing means selectively responsive to the code rate at which pulses of energy are received by said other decoding means from the section rails, means controlled by the said other decoding means at the said given end of each section for rendering ineffective the feed back code transmitting means at the adjacent opposite end of the next adjoining section when an opposite-togiven end moving train enters said stretch and shunts the rails of the first-encountered one of said sections, supplemental means at the said opposite end of each section rendered effective by the sections master decoding means when such means becomes inactive due to a removal of the said master code energy from the rails of the section for applying to the section rails special code energy in the form of recurrent code cycles each consisting'of an on and an ofi interval during which energy is and is not present respectively in the track rails and which energy is coded at one code rate or another according to traffic conditions beyond the opposite end of that section, and means controlled by the master decoding means at the said opposite end of each section for removing the master'code energy from the track rails of the section next adjacent to the sections said opposite endwhenever a givento-opp'osite end moving train entersthe stretch and shunts the rails of the first-encounteredone 40 of said sections, thereby to cause said special code energy to be applied to each of said sections intermediate the train and the extreme opposite end of the stretch.

11. In combination, a stretch of railway track including a pluralityof successive adjoining track sections, a first direction track circuit for each 'of-said sections comprising means at the 'sec,

tions given end for applying to the section rails master track circuit energy coded atone or another of a plurality of code rates each comprising a recurrent code cycles consisting of an on and an off interval during which energy is and is not present respectively in the section rails and master decoding means receiving energy from [the section rails at the opposite end of the section I back code transmitting means at the sections said opposite end controlled by the sections master decoding means and effective when and only when said master decoding means receives master code energy from the section rails for applying to such rails pulses of feed backenergy that occur in step i with the off intervals of said master code energy and other decoding means at the sections said given end receiving energy from the section rails and. including means selectively responsive to the means becomes inactive due to a removal of the said master code energy from the rails of the section for applying to the section rails special code energy in the form of recurrent code cycles each consisting of an on and an off interval during which energy is and is not present respectively in the track rails and which energy is coded 'at one code rate or another according to trafic conditions beyond the opposite end of that section, and means controlled by the master decoding means at the said opposite end of each section for removing the master code energy from the track rails of the section next adjacent to the section's said opposite end whenever a given toopposite end moving train enters the stretch and shunts the rails of the first-encountered one of said sections, thereby to-cause said special code energy to be applied to each of said sections intermediate the train and the extreme opposite end of the stretch.

12. In combination, a stretch of railway track including a plurality of successive adjoining track sections, a first direction track circuit for each of said sections comprising means at the sections given end for applying to the section rails master track circuit energy coded at one or another of a plurality of code rates each comprising recurrent code cycles consisting of an on and an off interval during which energy is and is not present respectively in the section rails and mas- -ter decoding means receiving energy from the section rails at the opposite end of the section and including means selectively responsive to the rate at which energy there received is coded,

means controlled by the master decoding means at the said opposite end of each section for reflecting the trafiic conditions in the stretch in the 'given-to-opposit'e direction by selecting the code rate at which master code energy is applied to the rails of the section next adjacent to that sections said opposite end, means controlled by'the master decoding means of said seccode rate at which pulses of energy are received tions in accordance with the code rate of the master code energy in the associated "sections for governing traihc moving over said stretch'in said given-to-oppo'site direction, a second direction track circuit for each section comprising feed back code transmitting means at the sections said opposite end controlled by the sections master decoding means and effective when and only when said master decoding means receives master code energy from the section rails for applying to such rails pulses of feed back energy that occur in step with the off intervals of said master code energy and other decoding means at the sections said given end receiving energy from the section rails and including means selectively responsive to the code rate at which pulses of energy are received by said other decoding means from the section rails, means controlled by the said other decoding means of said sections in accordance with the code rate at which energy is received by such means from the rails of the associated sections for governing traflic moving over said stretch in the opposite-to-given direction, means controlled by the said other decoding means at the said given end of each section for rendering ineffective the feed back code transmitting means at the adjacent opposite end of the next adjoining section when an opposite-togiven end moving train enters said stretch and shunts the rails of the first-encountered one of said sections, supplemental means at the said opposite end of each section rendered effective by the sections master decoding means when such means becomes inactive due to a removal of the said master code energy from the rails of the section for a plying to the section rails special code energy in the form of recurrent code cycles each consisting of an on and an oil interval during which energy is and is not present respective- "ly-in the track rails and which energy is coded at one code rate or another according to traffic conditions beyond the opposite end of that section, and means controlled by the'master decoding means at the said opposite end of each section for removing the master code energy from the track rails of the section next adjacent to the sections said opposite end whenever agiven-toopposite end moving train enters the stretch and shunts the rails of the first-encountered one of said sections, thereby to cause said special code energy to be applied to each of said sections intermediate the train and the extreme opposite end of the stretch.

FRANK H. NICHOLSON. 

